The invention relates to an electric toothbrush with an electric motor, which generates a motion of rotation and has a motor shaft, a gear that converts the motion of rotation into a reciprocating stroke, and a slip-on brush, which is to be attached to a handle segment so as not to be rotatable in said handle segment and which has a reciprocatable toothed rack in order to drive the rotatable bristle carriers.
Such an electric toothbrush is the subject matter of the EP-B-O 254 397. In the case of the toothbrush known in this document a contrate gear, which is driven by means of a pinion by the electric motor in the handle segment, is disposed in an eccentric, from which a crank arm leads to a reciprocatable connecting rod that leads out of the handle segment. This connecting rod couples with a toothed rack in the slip-on brush, when said brush is slid on the handle segment. The toothed rack generates in turn an alternating motion of rotation of the individual bristle carriers in the brush head.
If one wants to attain an adequately long stroke of the toothed rack, so that the bristle tufts exert more than one rotation at each stroke, the connecting rod leading out of the handle segment must execute an equally long stroke. That requires an eccentric, which is offset on the contrate gear by half the stroke. The result is automatically a relatively large diameter of the contrate gear, so that the diameter of the handle segment, too, must be correspondingly large, a feature that is often undesired.
The problem on which the invention is based is to design an electric toothbrush of the aforementioned kind in such a manner that its gear can be arranged to convert the motion of rotation of the electric motor into a reciprocating motion even while generating a longer stroke in toothbrushes with a small diameter.